Kinetic Investigation of Pd(II)-Catalyzed Ortho C-H Iodination of Benzamide with I2

Abstract

Abstract Intimate kinetic investigation of Pd(II)-catalyzed ortho C-H iodination of benzamide substrate via cyclopalladation was performed for the first time by using molecular I2 as a sole oxidant and acetate as a base. The reaction rate of the cyclopalladation step is independent of benzamide concentration but increased with an increase in acetate concentration and then gradually decreased due to blocking on coordination sites of Pd(II) by acetate. On the other hand, the reaction rate of the subsequent iodination step was first-order with respect to I2 concentration. Though the total activation energies of the cyclopalladation and iodination processes are comparable, it is reasonable that the cyclopalladation appears to be the rate-determining step of Pd(II)-catalyzed ortho C-H iodination, in which substrates, I2, and acetate are used in large excess. From the present results, it can be proposed that a minimum amount of acetate required for deprotonation of amide and ortho proton for cyclopalladation and rather excess I2 should be used to provide acceleration and high performance of Pd(II)-catalyzed ortho C-H iodination.